Feed pellets for fish and animals are manufactured on an industrial scale in a multi-stage process. The porosity or specific gravity of completely formed feed pellets or product may be an important criterion for quality of several types of food and feed products, including feed pellets for reared fish. The porosity of the product is of importance to the possibility of adding liquid nutrients which are absorbed into the product; the porosity is further of importance to floating capacities in a suitable medium, and it is of importance to the texture criterions like crispness, mouth sensation and toughness. To pellets of fish feed the porosity is important with respect to the ability of the pellets to absorb oil in the production process, and for the floating capacity/buoyancy in water on feeding.
Existing methods of manufacturing are hard to control accurately, in order for the product to have the desired porosity, or sufficient porosity for the products, feed substances, and/or feed pellets to achieve a desired absorption of fat.
For some products it will be important to be able to control the production process towards a minimum of expansion in, for example pellets, whereas the opposite will be the case for other products. In producing, among other things, feeds for pets such as for example dogs and cats, and feed for reared fish, this possibility of controlling the degree of expansion/porosity is essential, because the aim is often to enable addition of as much fat/oil as possible in a subsequent processing stage for pellets to be fed to fish. For fish feed the control of its degree of expansion is particularly important because such feed should, in addition, exhibit defined sinking capabilities in water after its fat/oil absorption.